Investigating the host binding signature on the Plasmodium falciparum PfEMP1 protein family.

The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family plays a central role in antigenic variation and cytoadhesion of P. falciparum infected erythrocytes. PfEMP1 proteins/var genes are classified into three main subfamilies (UpsA, UpsB, and UpsC) that are hypothesized to have different roles in binding and disease. To investigate whether these subfamilies have diverged in binding specificity and test if binding could be predicted by adhesion domain classification, we generated a panel of 19 parasite lines that primarily expressed a single dominant var transcript and assayed binding against 12 known host receptors. By limited dilution cloning, only UpsB and UpsC var genes were isolated, indicating that UpsA var gene expression is rare under in vitro culture conditions. Consequently, three UpsA variants were obtained by rosette purification and selection with specific monoclonal antibodies to create a more representative panel. Binding assays showed that CD36 was the most common adhesion partner of the parasite panel, followed by ICAM-1 and TSP-1, and that CD36 and ICAM-1 binding variants were highly predicted by adhesion domain sequence classification. Binding to other host receptors, including CSA, VCAM-1, HABP1, CD31/PECAM, E-selectin, Endoglin, CHO receptor "X", and Fractalkine, was rare or absent. Our findings identify a category of larger PfEMP1 proteins that are under dual selection for ICAM-1 and CD36 binding. They also support that the UpsA group, in contrast to UpsB and UpsC var genes, has diverged from binding to the major microvasculature receptor CD36 and likely uses other mechanisms to sequester in the microvasculature. These results demonstrate that CD36 and ICAM-1 have left strong signatures of selection on the PfEMP1 family that can be detected by adhesion domain sequence classification and have implications for how this family of proteins is specializing to exploit hosts with varying levels of anti-malaria immunity.

Quantification of methicillin-resistant Staphylococcus aureus strains in marine and freshwater samples by the most-probable-number method.

Recreational beach environments have been recently identified as a potential reservoir for methicillin-resistant Staphylococcus aureus (MRSA); however, accurate quantification methods are needed for the development of risk assessments. This novel most-probable-number approach for MRSA quantification offers improved sensitivity and specificity by combining broth enrichment with MRSA-specific chromogenic agar.

Methicillin-resistant Staphylococcus aureus from Northwest marine and freshwater recreational beaches.

The aim of the study was to determine the spatial distribution of methicillin-resistant Staphylococcus aureus (MRSA) at two marine and one freshwater recreational beaches in the Seattle area. Fifty-six marine water, 144 freshwater, and 96 sand samples were collected from June through August 2010. Isolates were biochemically verified as MRSA. Staphylococcal cassette chromosome mec (SCCmec) typing, multilocus sequence typing (MLST), pulse field gel electrophoresis and the presence of other antibiotic resistance genes were determined. Twenty-two freshwater (15.3%; n = 144), one dry sand (1.9%; n = 53), six wet sand (14%; n = 43), and two marine water samples (3.6%; n = 56) were MRSA positive. Of the 27 freshwater stream sites sampled multiple times, 37% of the sites were positive for MRSA and/or S. aureus ≥ 2 times. Twenty-one (67.7%) of 31 MRSA were SCCmec type IV, 15 (48.4%) of the isolates had MLST types not previously associated with humans, and 29 (93.5%) of the isolates carried other antibiotic resistance genes. This study is the first to report and characterize repeated MRSA-positive samples from freshwater drainages and creeks surrounding popular recreational beaches.

Survival of environmental and clinical strains of methicillin-resistant Staphylococcus aureus [MRSA] in marine and fresh waters.

Recent studies have found variable levels of methicillin-resistant Staphylococcus aureus [MRSA] in marine water from temperate and warmer climates suggesting that temperature may play a role in survival of MRSA in the environment. The aim of the study was to compare the survival of clinical and environmental MRSA and MSSA strains in fresh and marine water incubated at 13 °C and 20 °C over 14 days. Seven different MRSA strains and the MSSA ATCC 25923 were tested. Individual strains were diluted in sterile saline to a 0.5 McFarland standard (10(8) cfu/ml), serially diluted in duplicate to a final concentration of 10(5) cfu/ml in pooled filter-sterilized marine or fresh water and incubated at 13 °C or 20 °C in the dark. The results of this study found that temperature and salinity are important factors in MRSA and MSSA survival; the decay rate was ∼28% higher at 20 °C versus 13 °C and ∼34-44% higher in fresh water versus marine water. There was no statistical difference between environmental and clinical MRSA strain survival [P = 0.138]. The study found that MRSA/MSSA survival was significantly longer in marine water at 13 °C typical of the Pacific Northwest, which may have important implications for recreational beach visitors in colder climates.